Centurion-transport devices have no static descriptor and are not
receiver-paired, so their kind was only resolved by an online feature
scan. A headset powered off when Solaar started showed no kind, hence
no headphone icon in the tray/window — unlike receiver-paired mice and
keyboards, whose kind comes from the receiver's persistent pairing
registers.
Every Centurion-transport device seen so far is a headset, and the
centurion flag is known at construction time. Seed _kind=headset there
so the icon is correct offline and on first run. Drop the now-dead
online _infer_kind_centurion() feature scan and its Centurion branch
in the kind property.
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